Microsurgery includes any operation that uses visual magnification of a target structure to enhance the performance of a procedure, in which surgical microscopes are a primary vision system. Thanks to its minimal invasiveness, less trauma, less postoperative pain, and fast recovery, the microsurgery is widely used in various fields such as neurosurgery, reconstructive surgery, peripheral vascular surgery, and ophthalmology.
Three-dimensional vision provides more informative and intuitive observation of scene and precise interaction with environment than monocular vision does. Since microsurgery requires extremely precise hand-eye coordination and minute manipulation, three-dimensional microscopic vision system becomes indispensable element in microsurgery. A simple surgical binocular microscope comes with a pair of microscope eyepieces that provides binocular parallax and has been widely used for a long time. However, it can cause eye-strain, fatigue, and back and cervical pain for prolonged uses. Three-dimensional display devices can make these problems avoided.
Further, conventional microscopes have a low axial resolution, or a short depth of field, which generate blurred images in out-of-focus area. Microsurgery requires high resolution images in both lateral and axial directions. Confocal microscopes (U.S. Pat. No. 5,032,720) can satisfy these requirements and also provide depth information, in which a point of interest is illuminated by a point source of light using a pinhole aperture. Typically, this type of microscopes first scans an object point by point, and integrates this information to generate a complete image using an image processing system. Due to the complicated procedure, a slow imaging process is unavoidable in confocal microscopes. Further, they tend to have bulky and complicated structures.
Majority of three-dimensional display systems use the binocular parallax phenomena as well. Two images that are taken from two microscopes equipped with imaging systems (i.e. cameras) at the same time in different viewing angles are displayed in a three-dimensional display system. In a stereoscopic display system, these images are displayed in turns with a fast refresh rate. Three-dimensional images can be seen using a head mounted LCD shutter device or an overhead monitor through polarized glasses. These special eye-wears can cause discomfort and image degrading effect such as image flickering and low brightness. In an autostereoscopic display system, stereoscopic images are displayed simultaneously by dividing a two-dimensional display into two sets of pixels. Using parallax barriers, they create windows, in which each eye can see an only intended image. Autostereoscopic device does not require a special eye-wear but there are limits on the viewing angle and range.
In the image-guided surgery, preoperative medical images from multiple imaging devices such as magnetic resonance imaging (MRI), computer tomography (CT), ultrasound, and angiography, are employed in both diagnosis and treatment. These images reveal anatomical abnormalities such as tumors, infection, sclerosis, torn ligament, and osteoporosis as well as other anatomical structures in two-dimensional sectional or three-dimensional volumetric view.
To maximize accessibility and usability of these preoperative images during an operation, these images are registered with each other, with patient, with tracking instrument, and with intraoperative real-time microscope video image. Through the registration process, some of preoperative images and intraoperative video images are overlapped and displayed together so that a surgeon can observe underlying structures as well as surface structures during the operation, which can prevent unnecessary damages on the normal structures.
Registering a preoperative image with intraoperative stereoscopic video images and displaying them together in the stereoscopic display devices can be complicated because the preoperative image needs to be transformed into the data format that stereoscopic display devices require. Also, the transformation from a three-dimensional volumetric image to two-dimensional flat images can cause loss of valuable information.
There exist other types of three-dimensional display systems. Holography is a three-dimensional display method that generates a real image in the space (U.S. Pat. No. 5,266,531). Holography has been used for three-dimensional image display very limitedly due to its technical complexity and high manufacturing cost.
U.S. Pat. No. 4,834,512 to Austin discloses a three-dimensional display having a dimensional display, a fluid-filled variable focal length lens, and control device for manipulating the display and the lens. The two-dimensional display sequentially presents two-dimensional images that represent the cross sections of an object at different image depths. The fluid-filled variable focal length lens is disposed in front of the two-dimensional display and has a membrane that responds to the pressure of the fluid within the lens. Austin's display has a disadvantage that the display is unsuitable for displaying realistic three-dimensional images because the focus changing speed of the fluid-filled lens is slow.
U.S. Pat. No. 5,986,811 to Wohlstadter discloses an imaging method and system for creating three-dimensional image from a two-dimensional image having a plurality of image points. The imaging system includes an array of micro-lenses having variable focusing length, and means for holding the micro-lenses in alignment with the image points of the two-dimensional display.
A new image-guided microsurgery system comprising a imaging and a display system must satisfy current demands including providing three-dimensional image with a variable field of view, reducing eye fatigue, watching by multiple viewers, two-dimensional/three-dimensional compatibility, color expression and resolution that equal to or exceed those of HDTV, low manufacturing cost, and no significant data amount increase.